Typical post-tensioning construction is a construction method tier inserting a PC steel material into a cylindrical sheath previously embedded in concrete, and tensioning and fixing the PC steel material to provide the concrete with compressive stress by a reaction force of the tensile force, which compensates for a drawback of concrete in that the tensile strength is weak.
In this post-tensioning construction, a grout material, such as cement milk, is injected or mixed between the sheath and the PC steel material to achieve adhesion between the PC steel material and concrete, and to prevent corrosion of the PC steel material.
The operation of injecting the grout material is troublesome because it is performed in a construction site, and results in cost increase. Therefore, a pregrouted PC steel material previously provided with a sheath, a PC steel material and a grout material is in use. The pregrouted PC steel material has a PC steel stranded wire in which a plurality of steel wires (element wires) are stranded together, a pregrout layer disposed on the outer periphery of the PC steel stranded wire so as to accommodate the PC steel stranded wire, and a sheath covering the outer periphery of the pregrout layer (see Japanese Patent Laying-Open No 2003-172001 (PTD 1), paragraph 0005 and FIG. 2; Japanese Patent Laying-Open No 2007-211486 (PTD 2), paragraph 0017 and FIG. 1).
It is noted that, throughout the present specification a grout material used for a pregrouted PC steel material and a grout layer (a layer composed of the grout material) of the pregrouted PC steel material will be referred to as a pregrout material and a pregrout layer, respectively.
In the post-tensioning construction in which the pregrouted PC steel material is used, it is required that the pregrout material (pregrout layer) be not hardened until a PC steel stranded wire is tensioned (have a long pot life) and be hardened at ordinary temperature after the PC steel stranded wire is tensioned and fixed to concrete. As pregrout materials that may satisfy such required characteristics, various pregrout materials which are hardened within a predetermined period have been proposed.
For example, the above-described PTD 1 and Japanese Patent Laying-Open No. 2000-281967 (PTD 3) each propose a pregrout material having a predetermined number of days required for hardening, a predetermined composition and viscosity (claim 1 of each Patent Document). The number of days required for hardening is controlled by adjustment of the blending amount of a hardening agent that hardens the pregrout material.
On the other hand, Japanese Patent Laying-Open No. 2009-108497 (PTD 4) proposes a pregrout material composed of a thermoplastic resin composition. This pregrout material is softened by heating and is solidified by being left to cool.